Millions of tonnes of plastic debris dumped each year in the world's oceans continue to pose a lethal threat to whales after review of research literature from the last two decades reveals hundreds of cases in which cetaceans have been ill or killed by marine litter.

Entanglement in plastic bags and fishing gear have long been identified as a threat to smaller cetaceans but ingestion of such litter is also emerging as a serious cause of disability and death to whales. In 2008, two sperm whales stranded on the California coast were found to have 450 pounds of fish nets and other synthetic debris in their stomachs - one of which was ruptured stomach, and the whale had starved due to a large plug of wadded plastic blocking its digestive tract.

Seven male sperm whales stranded on the Adriatic coast of southern Italy in 2009 were stuffed with half-digested squids beaks, fishing hooks, ropes and plastic objects. Sperm and beaked whales are thought to be especially vulnerable because they are suction feeders but marine litter effects many different species of cetaceans including beaked and minke whales. Examination of gut contents for swallowed plastics after a dolphin or whale strands is rare and the majority of cetaceans that die from intestinal trauma getting caught up in fishing gear probably sink to the ocean floor.

In 2003, the United Nations Environment Programme (UNEP) established the Global Initiative on Marine Litter, but it launched a detailed analysis of the scope of the problem only in 2009.